This invention relates to a method and line for the high-speed packaging of pre-formed filter bags containing metered quantities of an infusion product such as tea, chamomile or similar herbs.
Patent application BO 2002 A000480 in the name of the same Applicant as this invention discloses an automatic machine for making and packaging filter bags containing an infusion product. The production process implemented by the machine comprises the steps of: forming the filter bag and related accessories consisting of tag and connecting thread; filling the infusion product into the bag; forming the protective envelopes in which the filter bags are individually wrapped; and packaging the filter bags into cartons in predetermined quantities. The process is performed continuously, without intermittent motion, and at very high speeds.
The process may be broadly divided into two consecutive sub-processes: in the first sub-process, the filter bag is fully formed and filled with a metered charge of the infusion product; the second sub-process involves packaging the filter-bags by forming the envelopes in which they are individually wrapped and then placing the wrapped filter bags in cartons or boxes.
The two sub-processes are performed in two separate parts of the machine along two separate filter bag paths connected by an intermediate path, all these paths lying in a single plane which, for convenience, will be called the process plane of the filter bags and which is vertical and longitudinal relative to the machine.
More specifically, the filter bags, as they move along the first path in the process plane of the machine, lie in a horizontal position, that is to say, transversal to the process plane itself.
In the second path, on the other hand, the filter bags move along the process plane of the machine in a vertical position, that is to say, parallel to the process plane.
In the intermediate path between the first and the second path, the filter bags are made to rotate by a turning unit one by one from the original position, transversal to the process plane, to the final position, parallel to the process plane.
The turning unit basically consists of two gripper wheels revolving about axes at right angles to the process plane and substantially tangent to each other. The first wheel is interfaced with the first path where the filter bags are advanced in a position transversal to the process plane. The second wheel, on the other hand, is interfaced with the second path where the filter bags are advanced in a position parallel to the process plane.
The two wheels of the turning unit counter-rotate at equal peripheral speeds.
The bags, picked up by the grippers of the first wheel, thus describe a circular arc as one with the first wheel and then, after reaching the area of tangency between the two wheels, are transferred one by one to the grippers of the second wheel which in turn transports them along another circular arc, with opposite concavity to that of the first arc, and which releases them one by one in the V-shaped fold of a strip of heat-sealable envelope material advancing along the second path of the filter bags which, as stated above, relates to the second sub-process.
The second sub-process basically comprises three steps, namely, sealing, cutting and cartoning. Sealing is performed both longitudinally and transversally to the strip of envelope material.
The longitudinal seal is performed continuously and involves joining the free longitudinal edges of the V-shaped folded strip, to form a sort of closed, flattened tube containing the filter bags at regular intervals from each other.
Transversal sealing, on the other hand, is performed intermittently and involves creating from the tube of heat-sealable paper a continuous series of separate compartments, each containing a single filter bag.
In the next step, the flattened tube is cut into separate lengths, each corresponding to a single filter bag.
The lengths of cut tube, constituting individually wrapped filter bags, are then fed to a cartoning unit which: checks them, counts them and places them in cartons.
A machine made in this way offers several important advantages, including that of working along the process plane of the machine with a continuous product flow and at a high production speed.
Machines of this kind have also proved capable of making the filter bags at speeds considerably higher than those of prior machines.
At present however, this potential cannot be utilized to the full because the packaging line is unable to operate at speeds as high as those of the forming line which makes the filter bags.
In fact, the timing of the sealing operations—especially the transversal seals—on the flattened tube from which the envelopes are made, poses a critical limit on current packaging lines.
The transversal seals require a minimum length of time which cannot be reduced below a certain threshold, dependent on the time required for the glue of the envelope material to soften and then re-solidify.
Another critical aspect preventing the packaging line from operating at the same high speeds as the forming line is the fact that the speed at which the strip of envelope material can be advanced is considerably lower (in the order of 30%) than the rotation speed of the turning unit.
Thus, each filter bag, after being released into the V-shaped folded strip of envelope material must be slowed positively and precisely. An expert in the trade will easily understand that further increasing the forming speed would require a highly complex mechanisms making it extremely problematic to slow the filter bag down with a degree of precision sufficient to correctly coordinate the exact point in time at which the filter bag is released at exactly the right point on the moving strip of envelope material.
Yet another critical aspect preventing the packaging line from operating at higher speeds to match those of the forming line is the fact that the higher the speed of the turning unit the higher the centrifugal forces in the curved paths of the filter bags, causing the infusion product in each filter bag to accumulate mainly on the bottom of the filter bag. That means the infusion product is not evenly spread inside the filter bags, causing bulges that make the filter bags too wide to fit properly inside the cartons in the required numbers, differing according to carton size, and thus creating packaging problems.